Heat treatment is used to change the mechanical properties, microstructure, and/or the residual stress state of metals or metallic components.
Traditional heat treatment techniques involve heating the component(s) either in a conventional air furnace or via gas jets. However, these techniques are inherently inefficient at transferring heat energy to the component(s).
This results in long cycle times due to the slow rate of heat transfer. In addition, the quality of the heat treatment is limited by the non-uniform heating of the component(s).
It is possible to overcome these disadvantages by using a fluidised bed furnace.
A fluidized bed is a bed of granular media that behaves like a fluid when a gas is passed through it. When employed in a furnace the medium is generally a refractory material, such as, for example, aluminium oxide.
The component to be heated is then submerged in the fluidised bed which is then heated.
By completely enveloping the component, the fluidized bed provides excellent heat transfer from the bed to the component being heated. For example a typical fluidised bed furnace has a heat transfer coefficient of approximately 390 W/m2/° C., while a typical gas jet type heating process might have a heat transfer coefficient of approximately 120 W/m2/° C.